Developments in internal combustion engines for motor vehicles focus on reducing exhaust emissions and fuel consumption. One approach for reducing fuel consumption and emissions is to adapt the operation of the various ancillary units, which also include the coolant pump, more precisely to the requirements of the engine. These efforts are aimed at more rapidly heating the engine following a cold start and at reducing the operational output needed for the coolant pump, in particular at a high rotational speed of the engine. Mass-produced designs such as electrically driven coolant pumps and switchable friction roller drives make considering other alternatives seem worthwhile with regard to cost and reliability. The split ring slider represents an approach, which has been known for decades, for influencing the delivery characteristics of turbines as well as compressors and pumps having a radial design, wherein an annular slider which encompasses the feed wheel of the pump on the outer circumference is axially shifted, forming an annular gap, and the flow cross-section on the outer circumference of the feed wheel therefore varies. The annular slider acts as a shutter in the outflow region of the feed wheel. Different solutions for activating the split ring slider are known.
CH 133892 B, for example, describes activating the split ring slider by directly using the pressure difference which is built up by the pump itself. It describes not only axially adjustable split ring sliders but also a rotationally adjustable split ring slider. The pump is not however adapted to the cooling requirements of the drive motor of a vehicle.
U.S. Pat. No. 1,813,747 B describes a multi-stage pump system comprising a split ring slider for the first stage which is rotationally driven by an external toothed wheel motor via a shaft and an externally toothed spur wheel. The annular slider is also in a threaded engagement in which an axial movement is superimposed onto the rotational movement of the annular slider. The external toothed wheel motor is steam-driven. Activating the annular slider in this way is not however suitable for adjusting the delivery volume of coolant pumps in motor vehicles.
An annular slider which is activated by means of pressurized air is known from DE 2007 019 263 B3. Such pneumatic designs require a connection to a pressurized air source, which in many installation situations is problematic.
In a coolant pump such as is known from WO 2009/138058 A1, the split ring slider is hydraulically adjusted by means of an electromagnetically operated axial piston servo pump. Generating the reciprocating piston movements electromagnetically requires a significant amount of energy, the design of the servo pump is elaborate and the electromagnetic piston drive is temperature-sensitive.
WO 2009/143832 A2 discloses an adjustable coolant pump for motor vehicles which is driven via the ancillary unit belt drive of the engine. With the aim of being able to employ the pump at high ambient temperatures and in restricted installation spaces and to manufacture it in a simple and standardisable and therefore cost-effective way, wherein the pump should also require only a small drive output and should not need to be filled, free of air, at the factory and should exhibit a favorable fail-safe characteristic, it is proposed that the split ring slider be activated hydraulically by means of the coolant via an axial piston pump which is arranged in the housing of the coolant pump. A reciprocating axial movement is impressed on the axial piston pump via a swash plate attached on the rear side of the feed wheel, wherein the reciprocating frequency of the reciprocating axial movement increases with the drive rotational speed of the coolant pump. The hydraulic working pressure thus generated is guided, via a magnetic valve which is opened when there is no current, onto an annular piston which the annular slider is fixedly connected to axially. A restoring spring acts counter to the hydraulic working pressure. The coolant pump comprises a relatively large number of individual parts which have to be manufactured and assembled to a high level of precision. It also has a large axial design length, which limits the design scope for arranging the coolant pump in the available installation spaces. Presumably for this reason, the drive shaft of the feed wheel is rotationally mounted by means of a roll bearing unit which has a large spatial distance from the feed wheel of the pump. This creates a high torque, caused by radial forces, at the roll bearing unit. A bearing clearance at the roll bearing which increases over the service life of the coolant pump due to wear also limits the extent to which the feed wheel can be guided exactly, such that the danger of the feed wheel rubbing against the annular slider or the suction feed of the housing of the coolant pump increases over its service life. This effect has to be counteracted by comparatively large circumferential gaps, from which the effectiveness of the coolant pump suffers. Lastly, the sliding contact between the swash plate and the axial piston also makes great demands on the wear resistance of the material used for them. The swash plate also exerts a transverse force on the reciprocating axial piston.
In addition to the split ring sliders which encompass the rotor wheel on the outer circumference, other designs for varying the geometry of flow cross-sections or flow profiles with the aim of adjusting the delivery volume are also known. The split ring slider is replaced with another setting structure in these designs, depending on the nature of the change in the geometry.
DE 10 2005 056 200 A1 for instance proposes an adjustable inflow sleeve using which an entry cross-section which leads into the inflow region for the feed wheel can be adjusted. It is adjusted by means of a wax thermostat. Material expansions in the wax material which are dependent on the temperature of the coolant are converted into axial adjusting movements of the inflow sleeve which acts as a cross-section-altering inflow shutter in the inflow region. One's ability to control the delivery volume is however limited when using a wax thermostat. The flow in the inflow region is also disrupted, and the switching speed is comparatively low.
U.S. Pat. No. 4,828,455 B provides a guide plate as an adjusting structure which lies axially opposite the feed wheel and can vary the effective flow cross-section for the coolant via the diameter of the feed wheel by being axially adjusted. The guide plate is provided with breaches through which the vanes of the feed wheel protrude. If the guide plate is axially adjusted towards a base of the feed wheel, the axial width of the flow cross-section on the side of the guide plate which faces axially away from the feed wheel is increased between the inflow region and the outflow region. If the guide plate is adjusted away from the base of the feed wheel, the axial width of this effective flow cross-section is reduced. The delivery volume at a given rotational speed of the feed wheel is correspondingly increased and reduced. A wax thermostat is provided in the inflow region in order to activate the setting structure (the guide plate), wherein the coolant flows around the wax thermostat, and the temperature-induced material expansions in the wax material cause the guide plate to be axially adjusted.
DE 199 01 123 A1 discloses adjusting the delivery volume using an adjusting structure which is likewise formed, in a comparable way to U.S. Pat. No. 4,828,455 B, as a guide plate, i.e. as a setting structure which alters the axial width of the flow cross-section beyond the feed wheel. A wax thermostat is again used as the actuator. A setting structure is also disclosed which is arranged slightly downstream of the feed wheel in the outflow region and can alter a coolant exit cross-section in the housing.
WO 2010/028921 A1 also discloses adjusting the delivery volume by means of an axially movable guide plate. However, this setting structure is axially adjusted electromagnetically. The electromagnetic actuator is arranged on an axial end, facing away from the feed wheel, of a drive shaft which drives the feed wheel, and is connected to the setting structure via a plunger which extends axially through the hollow drive shaft.
Yet another type of adjusting structure is used in a coolant pump such as is known from DE 10 2008 027 157 A1, which is formed by adjustable guide vanes of a ring of guide vanes which encompasses the feed wheel and by a rotationally adjustable setting ring. The setting structure, i.e. the adjustable guide vanes and the setting ring, is adjusted by means of a lifting rod of an actuator, wherein it is mentioned that the actuator can be activated pneumatically, hydraulically, electrically or magnetically.
While DE 10 2008 027 157 A1 arranges the guide vanes such that they can be pivotally adjusted, U.S. Pat. No. 4,932,835 B discloses guide vanes which are arranged in the diffusor region of a centrifugal compressor and cannot be moved relative to each other and are rigidly connected to an axially adjustable annular cup. The setting structure formed by the annular cup and the axially projecting guide vanes can be axially adjusted by means of a hand wheel via a toothed wheel coupling, in order to vary the axial overlap between the feed wheel and the guide vanes.